The WDM (wavelength division multiplexing) system has been introduced for optical communication networks. For example, the WDM has been introduced so as to accommodate many wavelength paths that are used for point-to-point communication in the core network and then the WDM for metro and regional networks and the ROADM (Reconfigurable Optical Add Drop Multiplexer) have been widely applied.
As wavelength paths increase, many optical signals are multiplexed so that more services can be realized. As a result, a fault that occurs in the photonic physical layer enormously affects a plurality of upper level service layers. In addition, with the widespread introduction of use of the ROADM, strong demand has arisen for nodes in the wavelength path network having advanced functions, high reliability and reduced cost.
Patent Literature 1 presents techniques that improve the reliability of a wavelength path network.
FIG. 1 of Patent Literature 1 shows the basic configuration of a wavelength path division multiplexing optical transmission device (hereinafter simply referred to as “transmission device”) and an example of switching performed therein upon occurrence of a fault. FIG. 1 (b) of Patent Literature 1 shows a switching operation corresponding to a fault that occurs in optical transmitter 12-1; and FIG. 1 (c) of Patent Literature 1 shows a switching operation corresponding to a fault that occurs in transmission line 52-1.
First, the action of optical transmission device 12-1 performed when a fault occurs will be described.
Signal selection circuit 11 switches the signal output destination from optical transmitter 12-1 to optical transmitter 13-1 such that optical transmitter 13-1 provided as a secondary system operates as a primary system. Thereafter, wavelength multiplexing means 14 multiplexes wavelengths of optical signals transmitted from optical transmitters 12-2 to 12-m and 13-1 so as to generate a wavelength multiplexed optical signal and transmits the wavelength multiplexed optical signal to transmission line 52-1.
On the reception side, wavelength demultiplexing means 21 demultiplexes the wavelength multiplexed optical signal transmitted from transmission line 52-1 into optical signals of individual wavelengths and sends the optical signals of individual wavelengths to optical receivers 22-2 to 23-1, respectively. When individual optical receivers 22-2 to 23-1 accept the optical signals of individual wavelengths, they output the accepted optical signals to signal selection circuit 24. Signal selection circuit 24 switches the signal output destinations such that the signals received from optical receiver 23-1 are substituted for signals received from optical receiver 22-1.
Thus, communication that was performing before a fault occurred can be restored while the switching operation is being performed and after the communication is blocked.
Next, the operation of optical transmission device 12-1 performed when a fault occurs over transmission line 52-1 will be described.
Wavelength multiplexing means 14 multiplexes wavelengths of optical signals transmitted from optical transmitters 12-1 to 12-m so as to generate a wavelength multiplexed optical signal and then switches the output designation of the wavelength multiplexed optical signal from transmission line 52-1 to transmission line 52-2 that is the secondary system.
On the reception side, wavelength demultiplexing means 21 that has the same wavelength input and output characteristics as does wavelength multiplexing means 14 demultiplexes the wavelength multiplexed optical signal into optical signals at individual wavelengths and sends the optical signals at individual wavelengths to optical receivers 22-1 to 22-m, respectively.
Thus, the communication that was being carried out before a fault occurred can be restored while the switching operation is being performed and after the communication is blocked.
Although FIG. 1 of Patent Literature 1 shows the case in which there are two transmission lines that are the primary system and secondary system, a plurality of primary transmission lines may be used. Alternatively, as shown in FIG. 9 of Patent Literature 1, the network can be extended using optical add drop nodes.
FIG. 1A is a schematic diagram showing a transmission device presented in Patent Literature 1.
In FIG. 1A, signal selection circuits (optical matrix switches) 1501 and 1504 are disposed respectively between optical transmitter 1505 and wavelength multiplexing section 1502 and between wavelength demultiplexing section 1503 and optical receiver 1510 as shown in FIG. 3 (b), FIG. 5 (c), and FIG. 8 (c) of Patent Literature 1. The transmission side and the reception side are connected through three or more transmission lines (or networks) 1506 to 1509.
Optical signals of wavelengths λ1 to λ4 transmitted from optical transmitter 1505 are input to input and output ports P1 to P4 through optical matrix switch 1501, respectively.
Wavelength multiplexing section 1502 multiplexes the wavelengths of each optical signal having wavelengths λ1 to λ4, generates a wavelength multiplexed optical signal, and then outputs the wavelength multiplexed optical signal from path port #1. Thereafter, the wavelength multiplexed optical signal is input to path port #1 of wavelength demultiplexing section 1503 through transmission line 1506.
Wavelength demultiplexing section 1503 demultiplexes the wavelength multiplexed optical signal into optical signals of individual wavelengths, generates each of optical signals having wavelengths λ1 to λ4, and then outputs each of the optical signals having wavelengths λ1 to λ4 from input and output ports P1 to P4, respectively.
The individual optical signals having wavelengths λ1 to λ4 transmitted from wavelength demultiplexing section 1503 are received by optical receiver 1510 through optical matrix switch 1504.